in SQL server ERRORLOG, it showsError: 17194, Severity: 16, State: 1.The server was unable to load the SSL provider library needed to log in; the connection has been closed. SSL is used to encrypt either the login sequence or all communications....

How can I fix this error?

thanks

Are you using SQL Express DB? Normally, if u did install it with default settings the instance name is COMPUTERNAME\SQLEXPRESS

Second, assuming that your Server=.\\MSSQLSERVER is correct. Go to Management Studio and check if the UID has permission to login.